Configuring Zeus

We presented “Configuring Zeus: A case study of online crime target selection and knowledge transmission” at APWG’s eCrime 2017 conference this past week in Scottsdale Arizona. The paper is here, and the slides from Richard Clayton’s talk are here.

Zeus (sometimes called Zbot) is a family of credential stealing malware which was widely deployed from 2007 to 2012 or so. It belongs to a class of malware dubbed ‘man-in-the-browser‘ (a play on a ‘man in the middle attack’) in that it runs on end-user machines where it can intercept web browser traffic to extract login credentials or to manipulate the page content displayed to the user.

It has been used to attack large numbers of sites, mainly banks — its extreme flexibility is achieved with ‘configuration files’ that indicate which websites are to be targeted, which user submitted fields are to be collected, what webpage rewriting (so called ‘webinjects’) is required and where the results are to be sent.

The complexity of these files seem to have restricted the number of websites actually targeted. In a paper presented at WEIS 2014 Tajalizadehkhoob et al. examined a large number of configuration files and described this lack of development and measured a substantial overlap in the content of different files. As a result, the authors suggested that offenders were not developing configuration files from scratch but were selling, sharing or stealing them.

We decided to test out this conjecture by seeking out messages about Zeus configuration files on underground forums (many of these are have been scraped, leaked or confiscated by law enforcement) — and this paper describes how we found evidence to support all three mechanisms: selling, sharing and stealing.

The paper also gives an account of the history of Zeus with illustrations from the messages that were uncovered along with clear evidence the release of tools to decrypt configuration files by security researchers was also closely followed on the forums, and assisted offenders when it came to stealing configuration files from others.